Some embodiments described herein relate to apparatus and methods for monitoring an implant, and in particular to apparatus and methods for detecting optical signals emitted from an implant with restriction of off-axis light.
Some embodiments described herein relate to apparatus and methods for monitoring an implant, and in particular to apparatus and methods for detecting optical signals through a relatively large surface area of tissue relative to a surface area of tissue through which an excitation optical signal is supplied.
The monitoring of the level or concentration of an analyte, such as glucose, lactate, oxygen, etc., in certain individuals is important to their health. High or low levels of glucose, or other analytes, may have detrimental effects or be indicative of specific health states. The monitoring of glucose is particularly important to persons with diabetes, a subset of whom must determine when insulin is needed to reduce glucose levels in their bodies or when additional glucose is needed to raise the level of glucose in their bodies.
A conventional technique used by many persons with diabetes for monitoring their blood glucose level includes the periodic drawing of blood, the application of that blood to a test strip, and the determination of the blood glucose level using calorimetric, electrochemical, or photometric detection. This technique does not permit continuous or automatic monitoring of glucose levels in the body, but typically must be performed manually on a periodic basis. Unfortunately, the consistency with which the level of glucose is checked varies widely among individuals. Many persons with diabetes find the periodic testing inconvenient, and they sometimes forget to test their glucose level or do not have time for a proper test. In addition, some individuals wish to avoid the pain associated with the test. Unmonitored glucose may result in hyperglycemic or hypoglycemic episodes. An implanted sensor that monitors the individual's analyte levels would enable individuals to monitor their glucose, or other analyte levels, more easily.
Some known devices perform in situ monitoring of analytes (e.g., glucose) in the blood stream or interstitial fluid of various tissues. A number of these devices use sensors that are inserted into a blood vessel or under the skin of a patient. Communicating and/or retrieving data from such known and/or proposed devices, however, can be challenging. For example, an implanted sensor may be able to communicate with a detector or receiver using radio frequency (RF) transmissions. Such a sensor, however, may require electronics, batteries, antennae, and/or other communication hardware which may increase the bulk of the implanted sensor, may require frequent inconvenient recharging, and/or may decrease the longevity or reliability of the implant.
A need therefore exists for apparatus and methods for detecting optical signals from an implanted sensor, such that a fluorescent sensor can be used. A fluorescent sensor may not require electric charging and/or transmission electronics. Such implanted sensors, however, may be difficult to read or to monitor optically because of low levels of florescence in the presence of high scatter due to dynamic changes in skin conditions (e.g., blood level and hydration). The skin is highly scattering, and the scattering may dominate the optical propagation. Scatter is caused by index of refraction changes in the tissue, and the main components of scatter in the skin are due to lipids, collagen, and other biological components. The main absorption is caused by blood, melanin, water, and other components.
Devices and apparatus described herein are suitable for providing accurate and consistent measurement of an analyte by monitoring an implantable sensor in such low-signal, high-scattering environments.